Add custom template loader class (#4706)

- Specifically to ignore caching for generated reports and labels
- Fixes https://github.com/inventree/InvenTree/issues/4611

InvenTree/InvenTree/settings.py

@@ -328,7 +328,7 @@ TEMPLATES = [
                 'InvenTree.context.user_roles',
             ],
             'loaders': [(
-                'django.template.loaders.cached.Loader', [
+                'InvenTree.template.InvenTreeTemplateLoader', [
                     'plugin.template.PluginTemplateLoader',
                     'django.template.loaders.filesystem.Loader',
                     'django.template.loaders.app_directories.Loader',

InvenTree/InvenTree/template.py

@@ -0,0 +1,36 @@
+"""Custom template loader for InvenTree"""
+
+import os
+
+from django.conf import settings
+from django.template.loaders.base import Loader as BaseLoader
+from django.template.loaders.cached import Loader as CachedLoader
+
+
+class InvenTreeTemplateLoader(CachedLoader):
+    """Custom template loader which bypasses cache for PDF export"""
+
+    def get_template(self, template_name, skip=None):
+        """Return a template object for the given template name.
+
+        Any custom report or label templates will be forced to reload (without cache).
+        This ensures that generated PDF reports / labels are always up-to-date.
+        """
+
+        # List of template patterns to skip cache for
+        skip_cache_dirs = [
+            os.path.abspath(os.path.join(settings.MEDIA_ROOT, 'report')),
+            os.path.abspath(os.path.join(settings.MEDIA_ROOT, 'label')),
+            'snippets/',
+        ]
+
+        # Initially load the template using the cached loader
+        template = CachedLoader.get_template(self, template_name, skip)
+
+        template_path = str(template.name)
+
+        # If the template matches any of the skip patterns, reload it without cache
+        if any([template_path.startswith(d) for d in skip_cache_dirs]):
+            template = BaseLoader.get_template(self, template_name, skip)
+
+        return template